1. Technical Field
The present disclosure relates generally to microwave applicators used in tissue ablation procedures. More particularly, the present disclosure is directed to a microwave applicator having a slidable jacket that acts an electrical termination choke.
2. Background of Related Art
Treatment of certain diseases requires destruction of malignant tissue growths (e.g., tumors). It is known that tumor cells denature at elevated temperatures that are slightly lower than temperatures injurious to surrounding healthy cells. Therefore, known treatment methods, such as hyperthermia therapy, heat tumor cells to temperatures above 41° C., while maintaining adjacent healthy cells at lower temperatures to avoid irreversible cell damage. Such methods involve applying electromagnetic radiation to heat tissue and include ablation and coagulation of tissue. In particular, microwave energy is used to coagulate and/or ablate tissue to denature or kill the cancerous cells.
Microwave energy is applied via microwave ablation antenna assemblies that penetrate tissue to reach tumors. There are several types of microwave antennas, such as monopole and dipole. In monopole and dipole antennas, microwave energy radiates perpendicularly from the axis of the conductor. A monopole antenna includes a single, elongated microwave conductor. Dipole antennas may have a coaxial construction including an inner conductor and an outer conductor separated by a dielectric portion. More specifically, dipole microwave antennas are typically long, thin inner conductors that extend along a longitudinal axis of the antenna and are surrounded by an outer conductor. In certain variations, a portion or portions of the outer conductor may be selectively removed to enhance the outward radiation of energy. This type of microwave antenna construction is typically referred to as a “leaky waveguide” or “leaky coaxial” antenna.
Conventional microwave antennas tend to have a narrow operational bandwidth, a wavelength range at which optimal operational efficiency is achieved, and hence, are incapable of consistently maintaining a predetermined impedance match between the microwave delivery system (e.g., generator, cable, etc.) and the tissue surrounding the microwave antenna. More specifically, as microwave energy is applied to tissue, the dielectric constant of the tissue immediately surrounding the microwave antenna decreases as the tissue is treated. The drop causes the wavelength of the microwave energy being applied to tissue to increase beyond the bandwidth of the antenna. As a result, there is a mismatch between the bandwidth of conventional microwave antenna and the microwave energy being applied. Thus, narrow band microwave antennas tend to detune over use hindering the effective delivery and dispersion of energy.
Various improvements have been disclosed in the art, which aid in maintaining proper tuning of the antenna during use as the tissue is treated. However, these improvements tend to compromise the structural integrity of the antennas, requiring additional enhancement and/or instrumentation instruments to facilitate insertion of the antenna intro the target treatment area.